This invention relates to a tunnel diode pulse generator and, more particularly, to a technique for triggering a tunnel diode.
Since the tunnel diode is one of the fastest electronic devices known, it is widely used for ultrafast time domain pulse measurements and applications. In such applications, the tunnel diode is used as a pulse generator to produce a step-like waveform. However, the tunnel diode is a two terminal device; and this leads to a number of problems. There is no input/output isolation. In shunt connections, whatever input voltage is present also appears in the output; and in series connections the input and output currents are equal. It is therefore difficult, in pulse generator applications, to isolate the trigger signal from the desired step-like transition, with the result that the trigger pulse causes distortions in the flatness of the pulse baseline and topline immediately before and after the fast pulse transition.
In typical prior art tunnel diode pulse generator circuit designs, the triggering impulse is added to the d.c. bias. When the triggering impulse strikes the tunnel diode, it then continues out on the output line. When the tunnel diode switches, a step transition is generated and propagates in both directions. Thus, the output signal propagating on the output line consists of the algebraic sum of the tunnel diode transition, which is desired, and the triggering impulse, which is not desired, resulting in the aforementioned distortions of the pulse baseline and topline.
The only commercial tunnel diode pulse generator solving the baseline-topline distortion problem employs a balanced differential capacitance probe arrangement for triggering the tunnel diode. However, this results in a 70 picosecond risetime which is too slow for many ultrafast pulse applications.